My builders have left a gap between the new stud and the old brick wall.

 

They have put in 100mm celotex type insulation which is the thickness of the stud but leaves the gap between.

 

Is this a problem, i cant help thinking this gap will be cold in winter and the expensive insulation will be useless.. 

25 minutes ago, learner said:

Is this a problem

 

Only if there is an air path from the heated space around or through the insulated studs. 

So its efficiency is dependent on the quality of the finished plaster board??

 

May sound silly but does the foil side go toward the brick wall or the room??

Has the builder sealed the insulation in the stud, as this is what makes the insulation work, either silicone/mastic/expanding foam and I put foil tape over mine as belt and braces. 

 

Ideally there should be a plastic sheet over the insulation, and behind the plasterboard to prevent warm moist air condensing on the rear of the insulation.

21 minutes ago, learner said:

So its efficiency is dependent on the quality of the finished plaster board??

 

No, I'll rephrase - Only if there is an air path from the warm side of the stud around or through the insulated studs.

 

The foil should be nearest the brick . It acts as a vapour check to reduce water vapour moving from warm to cold. 

So the foil side is always toward the outside of the building??

Celotex type insulation has the same covering on both sides

That’s correct 

If the stud is set off the wall The insulation should also be